Patent GB-1266038-A (GB)
IPC: G05D5/03
Filed: 1969-06-18
Abstract: 1,266,038. Automatic control systems. OWENS-CORNING FIBERGLAS CORP. June 18, 1969, No.30933/69. Heading G3R. An apparatus for modifying signals successively, representative of a sensed condition in an automatic control system, comprises a means responsive to input signals and further responsive to successive changes in said signal in one direction for limiting the effect of the changes to predetermined small amounts initially and means for adjusting the limits in response to successive changes in the signal, in a given direction. By limiting the signals after any change, undesired swings in control power are reduced. The apparatus includes means for comparing the magnitude of successive input signals and setting a predetermined limit on the magnitude of change of the signals passed by the apparatus to the output. Each signal is successively measured and passed to the output if no change has occurred but if the signal changes, the direction is detected and is passed up to a predetermined minimum limit, or alternatively the limit is increased if the signal successively changes in the same direction which increased limit applies to the next signal but not to the one presently passing through the apparatus. The apparatus may further compare a present limit with the amount of change at each measurement, and increase the limit if the change is larger than the previous measurement or decrease the limit if the change is smaller. In a particular embodiment shown in Fig. 5 in which the decision blocks are diamond shaped and action blocks are rectangular, the limit is successively doubled in response to successive increasing changes of input signal in the same direction. The input signal is received by a block 300 which compares it with the previous signal, and the difference passed to a logic block 301. If there is no change, a minimum limit stored in 303 via a gate 302 and gate 315 passes a signal unchanged to the output 317. If the next input signal increases, it is passed through block 305 to block 308 which decides whether the signal decreased last time. As it did not, the minimum positive limit is passed by block 307 to block 312 and compared with the signal. If the signal exceeds a minimum positive limit this is doubled and passed to a store 314 as the next limit and the last input to the apparatus plus the present limit is passed to output 317 via blocks 316. If the signal is smaller than the minimum positive limit then the signal is passed out unchanged through block 315. In the next sequence if the succeeding signal is greater than the doubled limit then this is doubled again et seq. If the signal decreases and is larger than the minimum negative limit then a new limit is passed and stored in unit 314 or if it is smaller then the minimum limit is retained. When the limits stored are other than the minimum, when the signals are decreasing towards the set point then the limits will be halved until the minimum is reached. The apparatus may be utilized in a system for controlling temperature and draw off a molten glass used to manufacture continuous fibres in order that the fibres may be of more uniform diameter than hitherto. The fibres are fed through orifices 20 in the bottom of a feeder 10. The temperature of molten glass is sensed by one or more thermocouples 42 the signal from which is amplified and converted into digits, then transformed and stored by apparatus 52, 53 as described above. The stored signal is sensed by a comparison unit I, and a correction signal is sent via units 54, 55 to control a saturable reactor 16 feeding a transformer - heater arrangement 10, 14. The fibre draw is controlled by a winder motor 38 which may be a frequency responsive variable speed motor supplied from a generator driven through a variable speed coupling 41 controlled by a ramp generator through circuits similar to those controlling the heater. Although the temperature and speed may be controlled as separate functions, comparison units I and II may be linked by a digital processing unit 62 which co-relates speed of draw with temperature. As the temperature adjusts itself more slowly than that of the speed, the former may be considered as a coarse adjustment and the latter a fine adjustment. Comparison units I, II may be arranged to take over control in the event of input signal failure, sensor failure or other fault. A sensor 63 enables one comparison unit to assume control while excluding control by the other. The limits may be alternatively increased geometrically or arithmetically.